1. Field of the Invention
The field of this invention resides within the industrial wire bonding art. More specifically, it relates to ultrasonically bonding a wire to a component such as an electrical, electronic, or semi-conductor part by an ultrasonic wire bonder. The ultrasonic wire bonder has wire fed to it from a reel which is then bonded by an ultrasonically vibratory transducer connected to a bonding tool. The invention specifically relates to providing an appropriate amount of wire to a bonder while at the same time maintaining control over the feed system to the bonder.
2. Prior Art
The prior art of wire bonding constitutes a number of wire bonders which receive large and small thickness wire to be ultrasonically bonded to a component. Such components can be electrical, electronic, or other types of components including many semi-conductor devices and processors in which a wire bonded connection must be undertaken. In such cases, wire is moved into proximity under a bonding tool with a transducer connected to it. This is done through a bonding head which moves in X, Y and Z directions.
Generally, the bonding head moves the bonding tool with the wire in proximity thereto into juxtaposition against an electrical device to be bonded. In doing so, the bonding head usually pays out a certain amount of wire from a reel.
The wire should be carefully and reliably removed from the reel or spool and then fed to the bonder as required. In some prior cases, the wire has been over fed or under fed. Such prior art dereelers created bonding problems with regard to the interaction of the bonding head, bonding tool, and movements of the bonding head.
In order to allow for a given amount of play in the wire as the bonding head moved, the prior art used a dancer-arm. This was used to tension the wire as it came off of the spool or reel as it was fed to the bonder. Because of the fact the dancer-arm provided tension through the use of a spring force it was subject to bonder induced vibrations. This created not only resistance problems but increased wear.
The system using the dancer-arm and other means for handling wire to place it in a properly fed tension mode caused the wire to break. Further to this extent, the tension required of the upstream tension on the wire provided by a spring force or dancer-arm created problems with regard to the movement of the wire on the downstream movement into the proximity of the bonding head. This led to wear problems downstream from the spring tensioners or dancer-arm. Further to this extent, the feeding of the wire to the bonding head through a tube or other feed system was such that it either could over feed or under feed the wire creating downstream problems of greater magnitude. The fundamental problems are such where the wire fed to the bonding head complicated the entire bonding operation and oftentimes was fouled, jammed, or improperly fed for a proper bond by the bonding tool.
This invention overcomes many of the drawbacks of the prior art in providing wire to a bonding head. In particular, this invention provides for proper torque and tension of the wire. It also provides for a buffer so that a proper amount of wire is always in readiness to be fed to the bonding head.
The foregoing features of the torque tension mechanism are provided by drawing the wire with a sufficient amount of tension from the wire spool. In this manner there will be a degree of pulling torque between the reel and the tensioner mechanism. This enhances the feed as well as the maintenance of the alignment of the wire coming from the reel or spool.
The buffer sensor of this invention creates a sufficient amount of wire within the entire feed system so that there is wire that can be fed without over amounts of slack. The wire to be fed is constantly monitored as to the amount of the necessary slack in the system for proper feeding to the bonding head. This constant monitoring through the buffer sensor of the invention allows for improved feeding, monitoring, and delivery of wire to the downstream end of the process namely to the bonder head.
For these reasons, the invention is a significant step over the prior art of bonding head wire dereelers for creating a wire bonding spool system and wire bonder of an improved type and capacity.
In summation, this invention comprises a wire bonding spool system having a torque and tension mechanism for tensioning the wire from a spool or reel in conjunction with a buffer sensor which senses and causes the wire to be fed with a proper amount of feed length between an over slack condition and a tightened over tensioned condition.
More specifically, the invention comprises a dereeler and control system for dereeling or unreeling wire from a spool for, or reel of wire that is to be bonded by a bonding head. The spool of wire is driven by an incremental movement of a motor which releases the wire on a basis of the required amount of wire.
In order to maintain tension between the spool and the feed system, a positive torque or tension mechanism is utilized comprising a pair of rollers that are driven by a motor. The rollers maintain positive tension on the wire being fed from the reel. At the same time, the roller axes are maintained in generally parallel relationship to each other. This allows for variously sized wire to be fed there through across a broad spectrum of thickness and width across the dimensions of the reel or spool from which the wire is fed.
The buffer sensor senses a certain amount of wire that is being fed. The buffer sensor incorporates a light responsive output reflected from the wire which is being fed. The wire being fed is passed through an opening, throat, or monitoring passage. As the wire passes with either undo slack or undo tension, the sensor puts out a signal that appropriately controls the feed of the wire from the reel.
The dereeler in combination with the bonding head also incorporates pinch rollers to properly feed the wire while at the same time monitoring the amount of wire that is being fed. This helps to assure the fact as to whether or not a proper bond has been undertaken downstream while at the same time monitoring the length of wire.
As will be seen from the following specification, this invention is a significant step over the art of providing wire to a wire bonder.